BOUNDARIES OF TYMPANUM. 



671 



auditory passage, and is united more closely to the osseous than the carti- 

 laginous portion; it is continued over the membrane of the tympanum in 

 the form of a thin pellicle. At the entrance of the meatus are a lew hairs. 

 In the subcutaneous tissue of the cartilaginous part of the meatus lie some 

 ceruminous glands of a yellow-brown color, resembling in form and ar- 

 rangement the sweat glands of the skin; these secrete the ear wax, and 



Fig. 238. 



VKRTICAT, SECTION OF THE MEATUS AFDITORIUS AND TYMPANUM (Scarpa). 



a. Cartilaginous part of the meatus. d. Cavity of the tympanum. 



b. Osseous portion. e. Eustachian tube. 



c. Membrana tympani. 



open on the surface by separate orifices : they are absent in the osseous 

 part, and are most abundant in that portion of the tube which is formed 

 by fibrous tissue. 



Vessels and nerves. The meatus receives its arteries from the posterior 

 auricular, the internal maxillary, and the temporal branch of the external 

 carotid. Its nerves are derived from the auriculo-temporal branch of the 

 fifth nerve, and enter the auditory passage between the bone and the carti- 

 lage (p. 96). 



INNER PARTS OF THE EAR. The internal constituents of the organ of 

 hearing are inclosed within the temporal bone, and consist of two large 

 spaces tympanum and labyrinth, with their accessory parts. 



The TYMPANUM, or drum of the ear (fig. 238, d), is a hollow interposed 

 between the meatus auditor iua and the labyrinth. It communicates with 

 the pharynx by a tube (e) (Eustachian), through which the air has ac- 

 cess ; and it is traversed by a chain of small bones, with which special 

 muscles and ligaments are connected. Minute vessels and nerves are 

 contained in the space. 



Dissection. The tympanic cavity should be examined in both a dried 

 and a recent bone. 



On the dry temporal bone, after removing most of the squamous portion 



